Mobile communications systems, such as cellular radio telephone systems, are typically realized as a network of neighboring radio cells which together provide complete coverage of the area to be serviced. Mobile radio subscribers may roam freely within the area of the system from one cell to another. One well known digital mobile radio system is the Global System for Mobile communication (GSM). Although the present invention is sometimes described using GSM terms, the present invention has wide application, and in any event, applies to any type of cellular or other mobile communications system.
Each cell is served by a base station that includes radio transceiver equipment. Plural base stations are interconnected via a switching node sometimes referred to as a mobile switching center (MSC) which also may be connected to other networks such as the public switched telephone network (PSTN).
Alternatively, several base stations may be controlled by a base station controller (BSC) connected between the base stations and an MSC. Typically, several BSCs are served by a single MSC which controls calls to and from other telephony and data communication networks. Whichever node (MSC or BSC) interconnects a group of base stations, that node controls radio-related functions such as paging, radio channel allocation, hand-over, and power control.
When a call is directed to a mobile station (MS) in the mobile communications system, that mobile station must be located and then paged before a call connection can be established. These tasks are facilitated by having idle mobile stations tuned to a base station control channel and by having the mobile stations periodically transmit registration messages over a base station control channel. As the mobile station moves from cell to cell, it retunes to the current cell's corresponding control channel.
In order to make the location and paging of subscribers efficient, cellular networks are often divided into location areas (LAs) where a location area includes a group of cells. As illustrated in FIG. 1, location area 4 (LA4) includes cells 1-6. In this example, five location areas LA1-LA5 make up a mobile switching center (MSC) service area. The MSC service area is associated with a visiting location register (VLR) database in which mobile stations currently within that service area are registered. When a call is routed to the MSC, the MSC checks the VLR to identify the current location area in which the called mobile station is registered. Thereafter, a paging message is distributed to those base stations in the identified location area and transmitted by base station transceivers within that location area.
As base station demands increase, the configuration of cells and sharing of equipment becomes more sophisticated. For example, FIG. 2A shows a single cell that employs a single omnidirectional antenna commonly used by all of the base station transceivers serving that cell. A more sophisticated configuration is shown in FIG. 2B where a single base station site serves three sectors or cells with each such sector cell having its own directional antenna. Each sector cell shares the same pool of transceiving equipment located at the base station site.
Even though the same pool of transceiving equipment is utilized for plural base station sectors, paging messages are sent from the MSC or BSC node to the base station site for each one of the sectors supported at that site. Thus, if the base station services three sectors, three separate but nevertheless identical paging messages are sent from the MSC or BSC to the base station site. This redundant message transmission creates unnecessary signaling, consumes transmission resources, and increases data processing loads. A similar problem exists for other types of control messages sent to some or all base station sectors, e.g., short messaging service (SMS) cell broadcast messages, system information messages used to inform mobile stations regarding network access procedures, etc.
It is an object of the present invention to overcome this problem and eliminate redundant or otherwise unnecessary signaling between nodes in a mobile communications system.
It is also an object of the present invention to minimize processor load associated with sending multiple messages to the same node.
It is a further object of the present invention to provide a single message from the MSC or BSC in a mobile communications system to a base station site and have the base station site transmit that message to multiple sectors supported by that site.
Yet another object of the invention is to improve the speed and performance of mobile radio paging operations.